As computing moves off the desktop into the hands of mobile users, it is becoming ever important for mobile devices to be aware of the user context. Important pieces of context include user's location, activities, nearby people and devices, and mode of transportation, if any. This knowledge can in turn be employed by mobile devices to display reminders, to configure themselves for use with other devices, and to behave in a manner that is appropriate for the surrounding environment (e.g., turn off cell phone ringer) or subcontexts of the surrounding environment such as whether particular states or transitions among states are occurring within the environment.
One aspect of context concerns whether or not the user (and the device) is inside or outside of a building or structure. For example, knowledge of such information can be used to facilitate determining the user's location (e.g., in a building or structure, in a particular building or structure, or in one of a set of known buildings or structures) and the user's mode of transportation (e.g., in a bus, car or airplane). Such knowledge can also be utilized to conserve power on systems that do not provide useful services inside buildings or outside.
Another aspect of the relevance of the loss of signals to a user's context and activities is related to a larger scale, that is, “urban canyons”—where GPS reception is poor because of surrounding structures. The loss of signals when a user moves from an area where signals are known to be receivable into an area where signals are known to be hard to receive can provide knowledge of where the user has traveled, currently is, and is potentially heading in an urban canyon. Urban canyons can be created by structures such as multi-story buildings (principally, and whether the user is inside or outside of the building), but also include trees, hills, and tunnels (generally). Knowledge of where GPS signals are lost can be of value to the user and to companies that seek to benefit economically by knowledge of the user location. To date, the loss of GPS signals or “GPS shadows” caused by structures has been considered a nuisance and deficiency. The GPS shadows are areas where a terrestrial receiver (e.g., a handheld receiving device) cannot receive adequate GPS signals due to signal blockage or degradation by any of the aforementioned structures (buildings, bridges, trees, hills, tunnels, etc.). There are currently unrealized benefits that can be obtained from the knowledge of shadow information and locations.